FIELD OF THE INVENTION
This invention relates to a greenhouse of an underground heat accumulation system in which radiant energy of the sun or wasted thermal energy is stored under the ground for use in heating the interior of the green-house.
Several different heating systems are available for greenhouses of the prior art, which systems include a stove system, a hot air system, a hot water system, a steam system and an electric heat system. They all depend on fossil fuel as the source of energy, and the amount of the thermal energy used for this purpose is constantly increasing with the development of cultivation of plants all the year round. Meanwhile the price of fossil fuel is also yearly increasing and this, combined with a shortage of oil, exerts serious influences on the greenhouse industry. Thus, the need to conserve energy by switching the source of energy elsewhere from the fossil fuel has been keenly felt. In view of this situation, there have recently been made various proposals to adopt a system of heating with accumulated thermal energy by utilizing the radiant energy of the sun or wasted thermal energy to meet the needs of the times. In this system, excess thermal energy that has not been consumed in the daytime is accumulated and released at night for heating purposes. Since this system is generally operated on day-to-day basis for accumulation and release of necessary thermal energy, the system suffers the disadvantage that it does not satisfactorily work when the amount of the accumulated thermal energy is small and inclement weather lasts in the wintertime in the absence of an ancillary thermal energy source. This would cause the temperature in the greenhouse to drop, thereby causing damage to the plants.